The present invention relates to electronic test apparatus and more particularly improved techniques for simulating dynamic loads for power sources under various load conditions.
In the past, power sources have been designed to meet and exceed expected load requirements based on an estimation of the type and power rating of particular loads that may be utilized under various circumstances. It has been found, however, that dynamic loads under actual use conditions often create such disturbance on a power source as to drive the source out of specification on modulation and harmonic distortion to the point of rendering the power source waveform incompatible with other equipment that may also receive power from the same source. In extreme cases the power source may be so disrupted by the load conditions as to prevent the satisfactory operation of the dynamic load itself on the distorted and modulating waveform. In situations where power supplies are to be subjected to a variety of load conditions, therefore, it is often desirable to be able to determine how a particular power source will respond prior to installation, particularly where the installation situs does not readily facilitate power source replacement, such as aboard ships, aboard airplanes, or in remotely accessible areas.
In order to reduce the possibility of installation of deficient power sources, various techniques have been proposed to simulate the dynamic loads on various power sources to insure the compatibility of power source and loads such that power source characteristics will remain within specification limits prior to installation. In one such prior known device, power line commutated silicon controlled rectifiers were used to provide pulsations off the alternating current of the power source. In operation, the SCR's would therefore act to provide pulsations representing a variety of dynamic load conditions limited only by the action of the SCR's. While the above technique was useful in providing a limited number of dynamic load conditions, the same technique was severely limited due to the inability of the SCR's to be turned on more than one time during each half cycle of the applied waveform. In addition, the same technique is incapable of being used compatibly with both AC and DC power sources and therefore limits the versatility of the simulation system. In either case, the system does not allow much variety in selecting the load conditions that may be encountered by the demand requirements of plural loads.
Still other prior known systems have been proposed which also simulate load conditions encountered by the various power sources during use. For the most part, however, each of the devices is designed to solve a particular problem unique to the load utilized or the power source to be tested, and is therefore very limited in the extent of its application as a simulation system.
Accordingly, the present invention has been developed to overcome the shortcomings of the above known and similar techniques and to provide an improved technique for enabling programmed load simulation representing current demand of an electrical load or combination of loads that might be encountered in a power distribution system.